In the utilization of complementary metal-oxide-semiconductor (CMOS) circuits it must be taken into consideration that the input potential of unconnected CMOS circuit inputs, or CMOS circuit inputs connected to tri-state circuits situated in the quiescent condition, is undefined, so that the CMOS transistors proceed into undefined operating conditions and can generate incorrect output signals. In order to prevent this situation, momentarily unused CMOS circuit inputs are to be connected to the one or to the other operating potential source of the CMOS circuit which can occur with the assistance of a correspondingly-dimensioned ohmic (pull-up or pull-down) resistor (McMOS Handbook, Motorola Inc., October, 1973, Chapter 6.D4, Page 6.15). Also simultaneously countered therewith is the further problem connected with the undefined input potential of CMOS circuits that, when such an input potential arrives in a critical region between the threshold voltage of the p-channel transistors and the threshold voltage of the n-channel transistors, both p-channel transistors and n-channel transistors can be highly conductive and can then be traversed by higher currents which causes destruction of the transistors after a short time.
Such ohmic pull-up or pull-down resistors can be provided in the form of external components with which the appertaining CMOS circuit inputs are connected. For reasons of space, however, such an external wiring is frequently not possible. Due to the ohmic connection of the input nodes to a fixed potential source which is then constantly established, on the other hand, an inherently possible integration of ohmic pull-up or pull-down resistors into the input structures of CMOS circuits no longer permits a measurement, in particular, the measurement of the input inverse currents, which is extremely important for the testing and technological evaluation of CMOS circuits.